1. Field of Technology
The present disclosure relates to cutting tools used in machining operations. More particularly, the present disclosure relates to removable drill heads, and drills including removable drill heads.
2. Description of the Background of the Technology
Drilling is a common metal cutting operation in which material is removed from a workpiece to provide a bore in or through a workpiece. Drilling is carried out by advancing a rotating drilling tool or “drill” into the workpiece in the direction of the drill's longitudinal axis. Thus, a drill may be defined as a rotating cutting tool used for machining bores in or through a workpiece. Common drill configurations include twist drills and spade drills. A twist drill is characterized by helical flutes disposed along at least a portion of the length drill and which terminate at a working end of the drill (the “drill tip”), which includes two cutting edges. A spade drill includes a wide cutting blade at the drill tip and lacks helical flutes along its length.
With respect to design, there are four main types of drills. A first drill type is a single-piece solid drill having either a twist drill configuration or a spade drill configuration. Such a drill typically includes cemented carbide material or hard steel and may include a cutting tip or “drill head” composed of a very hard material that is soldered or brazed to a steel shank. An example of such a drill is provided in European Patent Publication No. 0 353 214, which discloses a solid drill particularly useful for percussive drilling and that comprises a hard drill head brazed within a slot formed on a tool body. U.S. Pat. No. 6,601,659 discloses a solid twist drill having a spiral-shaped hollow body and a relatively hard cutting tip brazed to the body. Such a drill provides a lightweight design suited for applications subjected to substantial torsion and impact, such as occurs during drilling of concrete and brickwork. U.S. Pat. No. 6,655,882 discloses a single-piece solid twist drill including an elongate body and that is adapted for certain metal working applications. U.S. Pat. No. 7,267,513 discloses a single-piece solid spade drill including threads and adapted to increase productivity in certain drilling applications.
A second drill type is an integrated drilling tool comprising multiple indexable cemented carbide inserts secured by screws or other fasteners on a steel drill body. As is known in the art, an indexable insert may be removably secured to a holder in two or more cutting orientations, each cutting orientation presenting a different cutting edge. Thus, an indexable insert may be “indexed” to present a different cutting edge to the workpiece when a cutting edge in use has become unacceptably worn or damaged. In certain embodiments of this second drill type, several indexable inserts may be arranged on a single steel body to provide a partially overlapping cutting action and form a complete drill cutting geometry. Representative examples are provided in European Patent No. 1 280 625, which discloses an integrated drilling tool having two identical square-shaped carbide cutting inserts removably mounted on a steel body. U.S. Pat. No. 5,788,431 discloses an integrated drilling tool comprising at least one triangle-shaped carbide cutting insert removably mounted on a steel body. U.S. Pat. No. 6,527,486 discloses an integrated drilling tool having multiple generally rectangular-shaped carbide cutting inserts removably mounted on a steel body.
A third drill type is an integrated drilling tool comprising a single replaceable drill head having a twist drill or spade drill configuration made of either cemented carbide or a hard steel, and wherein the drill head is mounted on a steel drill body. An example is disclosed in U.S. Pat. No. 4,355,932, which describes an indexable, single-piece spade drill head mounted on a steel drill body. U.S. Pat. No. 6,044,919 also discloses a single-piece spade drill head mounted on a steel drill body. U.S. Pat. No. 6,224,302 is directed to a single-piece spade drill head having a V-shaped end intended to better ensure secure attachment on the drill's steel tool body. U.S. Pat. No. 7,241,089 discloses a single-piece spade drill head having an improved geometry including curved cutting edges, and wherein the drill head is mounted on a steel drill body. U.S. Pat. No. 7,306,410 teaches a single-piece twist drill head that is clamped on a steel drill body. Also, European Patent No. 1 280 625 discloses a single-piece twist drill head mounted on a steel tool body and secured in place by two screws.
A fourth drill type is a composite drilling tool comprising two different cemented carbide materials metallurgically bonded together. Examples include a solid drill comprising a relatively harder cemented carbide material in the drill's core region, and a relatively wear-resistant cemented carbide material in the drill's peripheral region. U.S. Pat. No. 6,511,265 discloses a composite solid twist drill including regions of different cemented carbide materials providing differing mechanical properties in the core and surface regions of the drill. United States Patent Application No. 2007/0042217 discloses a single-piece spade drill head having a relatively impact resistant cemented carbide grade in a center region, and a relatively wear resistant cemented carbide grade in a peripheral region, and wherein the different cemented carbide materials are metallurgically bonded together.
A problem limiting the performance of non-composite drills is that the cutting speed (speed of the cutting edge relative to the workpiece) varies from zero at the drill's center to a maximum cutting speed at the drill's periphery. Therefore, the conditions promoting wear on a drill's cutting tip can be significantly more aggressive at the periphery than at the center of the cutting tip. To address this problem, certain known composite drills include different carbide grades, having different properties, in the drill's central and peripheral regions. Such an arrangement can be adapted to optimize drilling performance. The manufacturing costs of composite drills, however, are relatively high because manufacturing the drill involves the pressing and sintering of at least two different cemented carbide materials.
Accordingly, it would be advantageous to provide a drill having a construction that improves drilling performance, but which does not require the costly steps involved in manufacturing composite drills including multiple (i.e., two or more) regions of cemented carbide materials.